This invention relates to a packaging machine and to a method of filling flexible pouches with product, purging air from the filled pouches, and then sealing the pouches.
In the packaging of certain products, and particularly food products, the filled and sealed pouches are delivered to an autoclave or retort and are heated to high temperatures so as to sterilize the product in the pouches. In order for this packaging process to be successful, it is important that the sealed pouch be substantially free of air when the pouch is delivered to the autoclave. If any significant amount of air is present in the pouch, the air will expand when subjected to the high temperatures in the autoclave and will cause the pouch to balloon, such ballooning sometimes destroying the seals of the pouch. Even if the pouch is not subjected to autoclaving, it is often desirable to remove the air from the pouch so that the product will be packaged in an oxygen-free environment and will possess a long stable shelf life.
One method of removing air from pouches is disclosed in Johnson United States application Ser. No. 247,253, filed Mar. 25, 1981 and entitled Machine And Method For Making Substantially Air-Free Sealed Pouches. In the system disclosed in the Johnson application, filled pouches are advanced beneath a steam nozzle and are subjected to a downward flow of steam which tends to drive air from the pouches. While each pouch is beneath the steam nozzle, a vacuum nozzle is inserted downwardly into the pouch and then the upper end portion of the pouch is closed around the vacuum nozzle to temporarily seal the pouch to the nozzle. A vacuum then is drawn through the vacuum nozzle to evacuate air from the pouch. While the pouch is still closed around the vacuum nozzle, the latter is retracted from the pouch and then the upper end portion of the pouch is closed and is heat-sealed. All of the foregoing operations preferably take place while steam is being directed downwardly toward the pouch. The steam tends to purge the pouch of air before the vacuum nozzle is inserted into the pouch, facilitates the drawing of a vacuum in the pouch by the vacuum nozzle, and prevents air from entering the pouch as the vacuum nozzle is retracted out of the pouch.
While the steam is beneficial from the standpoint of helping to reduce the air content of the pouches, the steam makes it difficult to form wrinkle-free top heat seals along the upper end portions of the pouch. The steam tends to soften and wilt the upper end portions of the pouches and thus makes the pouches susceptible to wrinkling. In the Johnson system, the upper end portions of the pouches tend to particularly wrinkle when the pouches are closed around the vacuum nozzle.